From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH net V2 1/2] tuntap: do not zerocopy if iov needs more pages than MAX_SKB_FRAGS Date: Tue, 30 Jul 2013 14:41:13 +0300 Message-ID: <20130730114113.GA22218@redhat.com> References: <1374116116-43844-1-git-send-email-jasowang@redhat.com> <20130719050335.GA8537@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: davem@davemloft.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Jason Wang Return-path: Content-Disposition: inline In-Reply-To: <20130719050335.GA8537@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Fri, Jul 19, 2013 at 08:03:35AM +0300, Michael S. Tsirkin wrote: > On Thu, Jul 18, 2013 at 10:55:15AM +0800, Jason Wang wrote: > > We try to linearize part of the skb when the number of iov is greater than > > MAX_SKB_FRAGS. This is not enough since each single vector may occupy more than > > one pages, so zerocopy_sg_fromiovec() may still fail and may break the guest > > network. > > > > Solve this problem by calculate the pages needed for iov before trying to do > > zerocopy and switch to use copy instead of zerocopy if it needs more than > > MAX_SKB_FRAGS. > > > > This is done through introducing a new helper to count the pages for iov, and > > call uarg->callback() manually when switching from zerocopy to copy to notify > > vhost. > > > > We can do further optimization on top. > > > > The bug were introduced from commit 0690899b4d4501b3505be069b9a687e68ccbe15b > > (tun: experimental zero copy tx support) > > > > Cc: Michael S. Tsirkin > > Signed-off-by: Jason Wang > > > Acked-by: Michael S. Tsirkin Was this patch dropped? Any objections to merging it for 3.11 and stable? > > --- > > The patch is needed fot -stable. > > --- > > drivers/net/tun.c | 62 ++++++++++++++++++++++++++++++++-------------------- > > 1 files changed, 38 insertions(+), 24 deletions(-) > > > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > > index 5cdcf92..db690a3 100644 > > --- a/drivers/net/tun.c > > +++ b/drivers/net/tun.c > > @@ -1035,6 +1035,29 @@ static int zerocopy_sg_from_iovec(struct sk_buff *skb, const struct iovec *from, > > return 0; > > } > > > > +static unsigned long iov_pages(const struct iovec *iv, int offset, > > + unsigned long nr_segs) > > +{ > > + unsigned long seg, base; > > + int pages = 0, len, size; > > + > > + while (nr_segs && (offset >= iv->iov_len)) { > > + offset -= iv->iov_len; > > + ++iv; > > + --nr_segs; > > + } > > + > > + for (seg = 0; seg < nr_segs; seg++) { > > + base = (unsigned long)iv[seg].iov_base + offset; > > + len = iv[seg].iov_len - offset; > > + size = ((base & ~PAGE_MASK) + len + ~PAGE_MASK) >> PAGE_SHIFT; > > + pages += size; > > + offset = 0; > > + } > > + > > + return pages; > > +} > > + > > /* Get packet from user space buffer */ > > static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, > > void *msg_control, const struct iovec *iv, > > @@ -1082,32 +1105,18 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, > > return -EINVAL; > > } > > > > - if (msg_control) > > - zerocopy = true; > > - > > - if (zerocopy) { > > - /* Userspace may produce vectors with count greater than > > - * MAX_SKB_FRAGS, so we need to linearize parts of the skb > > - * to let the rest of data to be fit in the frags. > > - */ > > - if (count > MAX_SKB_FRAGS) { > > - copylen = iov_length(iv, count - MAX_SKB_FRAGS); > > - if (copylen < offset) > > - copylen = 0; > > - else > > - copylen -= offset; > > - } else > > - copylen = 0; > > - /* There are 256 bytes to be copied in skb, so there is enough > > - * room for skb expand head in case it is used. > > + if (msg_control) { > > + /* There are 256 bytes to be copied in skb, so there is > > + * enough room for skb expand head in case it is used. > > * The rest of the buffer is mapped from userspace. > > */ > > - if (copylen < gso.hdr_len) > > - copylen = gso.hdr_len; > > - if (!copylen) > > - copylen = GOODCOPY_LEN; > > + copylen = gso.hdr_len ? gso.hdr_len : GOODCOPY_LEN; > > linear = copylen; > > - } else { > > + if (iov_pages(iv, offset + copylen, count) <= MAX_SKB_FRAGS) > > + zerocopy = true; > > + } > > + > > + if (!zerocopy) { > > copylen = len; > > linear = gso.hdr_len; > > } > > @@ -1121,8 +1130,13 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, > > > > if (zerocopy) > > err = zerocopy_sg_from_iovec(skb, iv, offset, count); > > - else > > + else { > > err = skb_copy_datagram_from_iovec(skb, 0, iv, offset, len); > > + if (!err && msg_control) { > > + struct ubuf_info *uarg = msg_control; > > + uarg->callback(uarg, false); > > + } > > + } > > > > if (err) { > > tun->dev->stats.rx_dropped++; > > -- > > 1.7.1